Tags are definitely making for search, but they are not utilized: one can only click on one tag, or depends on all the set of tags one selected: which generates too many results.
A tag group should be enabled to be used as a searching criteria.
You can always use e.g.
[c] [mysql] in the search field to find questions with those two tags.
That is, just add tag(s) in square brackets to the search field to filter found questions by that tag(s).